Mufflers are provided in exhaust gas systems of internal combustion engines to damp pressure surges which arise upon the fast opening of the outlet valves and to reduce noise emission. Different kinds of muffling devices are arranged in the interior of a muffler housing for the purpose of muffling. Examples of such devices include perforated pipes, chambers, insulating material and/or pipes with varying cross-sections. Further muffling devices are present in arrangements which divide the exhaust gas flow into a plurality of part flows of different lengths, whereby sound waves partly cancel one another out by phase-shifted superimposition due to interference effects.
A substantial proportion of the energy supplied by the fuel is lost in the form of heat energy through the exhaust gas system in internal combustion engines. It is advantageous in this respect to utilize at least a portion of this waste heat present in the exhaust gas and convert it into useful energy. There is only a limited construction space available for the exhaust gas system, particularly with internal combustion engines installed in motor vehicles. It is therefore frequently difficult to integrate devices required to utilize the waste heat into the exhaust gas system.